The present invention relates to a wafer and a method of working the same and, more particularly, to a novel wafer and method of working the same which can prevent defects such as the chipping of the joint regions between the contour of the wafer and the cut-away portion of the wafer such as an orientation flatness.
In general, in the production of a semiconductor device such as a transistor, an integrated circuit (IC) or a large-scale integrated circuit (LSI), when foreign matter including dust, chipping etc. adhere on the surface of a wafer, which is a substantially circular flat member made of a semiconductor material such as silicon (Si), when subjecting the wafer to processing such as diffusion, coating with a resist, etching and evaporation, the foreign matter causes scratches in the wafer surface and defects such as an nonuniform film thickness and drawbacks arise during transportation of the semiconductor device.
There are various causes for the appearance of such foreign matter. As one of the causes, it has been known that, for example, during the transportation of wafers the outer peripheral part of the wafer collides against any transport mechanism or the wafers come into contact with each other, whereby the outer peripheral part of the wafer itself breaks off locally. Chips resulting from the breakage adhere on the surface of the wafer as the foreign matter, to incur various defects. In order to prevent the aforementioned breakage of the outer peripheral part of the wafer, in, for example, Japanese Patent Application Publication No. 53-38594, both the major surfaces of the wafer outer-peripheral part have been chamfered by mechanical or chemical means.
However, it has been have found that, even when both the major surfaces of the wafer outer-peripheral part are chamfered in this manner, the wafer nevertheless frequently chips.
As a result of research efforts into the cause of chipping, important facts have been revealed. In general, a wafer is formed with a flat portion called the “orientation flatness (principal flatness)” by cutting a part of the wafer rectilinearly, in order to indicate the crystal orientation of the wafer and also to position the wafer. The formation of such flat portion, however, results in forming acute bends in the joint parts between the flat portion and the contour of the wafer. Consequently, the joint part is liable to chipping. That is, during the transportation of the wafer, the joint part collides against the guide of an air bearing or comes into touch with another wafer, whereby this joint part breaks off to give rise to chipping.
As described above, the acute bends are formed in the joint parts between the flat portion as the orientation flatness and the contour of the wafer. In this regard, it has been found that a harmful phenomena occurs in the regions of the acute bends. In the processing of the wafer, when a photoresist film for a photolithographic process is formed on the surface of the wafer, crowns and fringes appear in the photoresist film. When a thin film such as an epiaxially vapor-grown layer is formed on the wafer surface, a film of abnormal thickness is formed due to, e.g., abnormal growth.
It is accordingly an object of the present invention to provide a wafer and a method of working the same which can prevent the appearance of foreign matter and the occurrence of other various defects attributed to the chipping of the joint regions between the contour of the wafer and the cut-away portion of the wafer such as an orientation flatness.